Modulating noise produced by rotating bodies

ABSTRACT

Noise produced by a rotating apparatus having radially extending, spaced, load carrying elements, e.g. the tread design portions of a tire, is modulated by selectively pitching and sequencing load carrying elements. The array of load carrying elements are selected from at least two different pitch lengths, the ratio of pitch lengths being within a given range of (2n3)/(2n-1): 1.0, n 3, 4, 5 or 6. Noise is further modulated by utilizing strings of 3 or more consecutive load carrying elements having substantially the same pitch length. The length and sequential position of the strings modulates the natural load carrying element frequency. The invention is useful in the design of such apparatus as tread elements for tires, gear teeth, V-belt notching, fan blade spacing, and in other rotating apparatus.

United States Patent Vorih Dec. 16, 1975 MODULATING NOISE PRODUCED BYROTATING BODIES [75] Inventor: William J. Vorih, Denver, C010.

[73] Assignee: The Gates Rubber Company,

Denver, C010.

[22] Filed: Aug. 31, 1971 [21] Appl. No.: 176,460

[52] US. Cl. 152/209 [51] Int. Cl. B60C 11/08 [58] Field of Search152/209 V [56] References Cited UNITED STATES PATENTS 2,878,852 3/1959Lippmann et a1 152/209 3,023,798 3/1962 Moore et a1. 152/209 3,064,57810/1961 Braudonn 152/209 Primary Examiner.lames B. Marbert Attorney,Agent, or FirmCurtis l-l. Castleman, Jr.; Raymond Fink; H. W. Oberg, Jr.

[57] ABSTRACT Noise produced by a rotating apparatus having radiallyextending, spaced, load carrying elements, e.g. the

-tread design portions of a tire, is modulated by selectively pitchingand sequencing load carrying elements. The array of load carryingelements are selected from atleast two different pitch lengths, theratio of pitch lengths being within a given range of (2n3)/(2nl 1.0, n3, 4, 5 or 6. Noise is further modulated by utilizing strings of 3 ormore consecutive load carrying elements having substantially the samepitch length. The length and sequential position of the stringsmodulates the natural load carrying element frequency.

The invention is useful in the design of such apparatus as treadelements for tires, gear teeth, V-belt notching, fan blade spacing, andin other rotating apparatus.

13 Claims, 14 Drawing Figures US. Patent Dec. 16,1975 SheetlofS3,926,238

INVENTOR. WILLIAM VORIH FIG. 2

ATTORNEY V U.S. Patcnt DISC. 16, 1975 Sheet 2 of 5 PITCH RATIO O.667= LRELATIVE AMPLITUDE O lllllllll'l" |||n| llllll I00 n0 Izo I30 I40 I50I60 I70 I75 HARMONIC FIG. 3A

PITCH RATIO O.7I4:I.O

RELATIVE AMPLITUDE I00 IIO 0 I40 I50 1 I60 I70 I75 HARMONIC FIG. 3B

PITCH RATIO 0.75 L0 RELATIVE AMPLITUDE 5. Q J-IJ-II-I-I IOO no I20 I I II I I HARMONIC FIG. 3C

INVENTOR.

WILLIAM VORIH cw yawn}.

ATTORNEY US Patent 'Dec.16,1975 Sheet30f5 3,926,238

RELATIVE AMPLITUDEZO I I0 20 3O 4O 5O 6O 7O 75 HARMONIC FIG. 4

INVENTOR. WILLIAM VORIH ATTORNEY U.S. Patent Dec.16, 1975 Sheet4of53,926,238

a, PITCH LOCATION FIG. 5A

RELATIVE AMPLITUDE o 35 4o 45 so 55 so 65 7O HARMONIC FIG. 5B

2- PITCH J I LOCATION FIG. 6A

RELATIVE AMPLITUDE so 7O HARMONIC FIG. 6B

INVENTOR. WILLIAM VORIH ATTORNEY US. Patent Dec. 16, 1975 Sheet50f53,926,238

LOCATION FlG. 7A

RELATIVE 20 AMPLITUDE 0 I 4o s5 HARMONIC FIG. 78

Tim

LOCATION 5FIG. 8A

O as 40 45 5o 55 so e5 10 HARMONIC FIG. 8B

ATTORNEY MODULATING NOISE PRODUCED BY ROTATING BODIES BACKGROUND OF THEINVENTION This invention relates to pitching and sequencing techniquesas applied to rotating apparatus having radi-' ally extending loadcarrying elements spaced apart from one another. The invention moreparticularly relates to modulating noise produced by the rotating loadcarrying elements, e.g. individual tire tread design elements contactinga road surface.

As a tire rolls, its individual tread design elements cause airdisturbances upon impact with the road, cre--- ating a spectrum of audiofrequencies broadly referred to as tire noise. Each design elementcauses a pulse, itself devoid of tone; however, the interaction of allof the pulses creates what is interpreted as the noise. For any giventread design there is associated a particular quantum of energy. Thus,while it is impossible to reduce the amount of energy released by a tireas it strikes a road surface, it is possible and has been the goal ofmany investigators to reduce the amplitude of the noise producing peaksas displayed by the frequency spectrum of the tire and to distributethis energy over a wide frequency band, i.e. to approach white noise.

Various methods have been employed in the past to reduce noise generatedby tires, particularly tires having transverse tread portions such assnow tires. A common expedient has been to use a variety of differentpitch lengths for the tread design elements. It has also been common toutilize random or sinusoidal sequencing of the pitches in an attempt tomodulate the objectionable noise producing frequencies. Whilerepresenting an improvement over unpitched (i.e. equally spaced) treaddesigns, certain significant drawbacks are apparent. One such drawbackis that the tire molds become increasingly more expensive to manufactureas the number of different sipe elements increases, requiring a largeexpenditure for forming and bending dies to produce the necessary sheetmetal stampings. Also, the randomnessof the pitching sequence requiresthe use of relatively large, e.g. 180 mold segments which increases thecost of the hand carved models from which the molds are made. Anotherdrawback with these traditional pitching methods is that the treadfrequency, equivalent to the product of the tread frequency harmonic andthe rotation speed of the tire, is prevalent asa relatively highamplitude naked peak creating an objectionable noise.

. It has been another characteristic of the prior art to employmathematical methods for tuning out certain critical frequencies of atires noise spectrum by usually using an iterative process adapted to besolvedwith the aid of a computer program. The method customarilyinvolves shifting particular tread elements to shift the correspondingcritical peak frequencies to an adjacent hole frequency, thus levelingout and modulating the noise spectrum. Such a method is described in thepublication. Quietin'g Noise Mathematically Its Application to SnowTires,S.A.E.;paper No. 690520,

The state of the art is further exemplified by the tire treadconstruction technique shown in Pat. No. 3,023,798 to Moore et a1." t IIt is a primary object of the invention to reduce noise generated byrotating apparatus having radially extending load carrying elementswhich produce audible noise 2 frequencies, namely by utilizing aparticular pitch ratio between load carrying elements.

It is another object to modulate noise produced by rotating apparatushaving load carrying elements by pitching the load carrying elements andutilizing sequences of these pitches of such length and sequentialpositioning to modulate the load carrying element frequency harmonicproduced upon rotation of the apparatus.

It is still another object to utilize a minimum number of pitch lengths,preferably two, for use in a tire tread element to reduce cost andimprove the frequency spectrum produced by a tire impacting a roadsurface.

These and other objects are met and the disadvantages of the prior artare overcome by utilizing the apparatus and method of the presentinvention as more particularly described hereinafter.

SUMMARY OF THE INVENTION The noise spectrum produced by spaced rotatingload carrying elements of a rotating apparatus is modulated by providingthe apparatus with discrete pitch lengths in which the ratio of pitchlengths falls within the open intervals defined by the boundary nodalpoints (n-l )/n 1.0, (n being an integer selected from 2, 3, 4, 5 or 6),and excluding the ratios defined by the boundary nodal points. Furthermodulation is obtained by sequencing the individual pitches in such amanner that the sequence is characterized by a plurality of strings ofthe load carrying elements, each string consisting of at least threeconsecutive load carrying elements of substantially identical pitchlength. The length and sequential positioning of the strings areselected to modulate the load carrying element frequency harmonic whichis produced upon rotation of the apparatus.

The invention has a number of applications, including in V-beltnotching, machine tool cutters, circular saw blades, fan blade spacings,gear tooth spacing, and snow tire tread spacing design. In each of theseapplications, the apparatus consists generally of a member having moreor less radially extending and spaced rotatable load carrying elementsrotating about one or more axes.

BRIEF DISCUSSION OF THE DRAWINGS The invention will be more readilyunderstood by reference to the accompanying drawings, in which likenumerals designate like parts in the several figures, and wherein:

FIGS. 1 and 2 schematically depict fragmentary sections oftire treadelements having two pitchlengths in a particular ratio according to theinvention. 7

FIGS. 3A, 3B, and 3C depict, respectively, in graphic form the predictedform of the frequency response spectrum generated by three two-pitchedsnow tires having different pitch ratios.

FIG. 4 shows the tread frequency band produced by a two pitched tirehaving too high a pitch ratio.

FIG. 5 illustrates a prior art type of random pitch sequencing and FIG.5B the resulting frequency response.

FIGS. 6B, 7B and 8B compare in graphic form predicted frequencyspectrums produced by well pitched tires using varied sequential lengthsand positioning of tread design elements shown in FIGS. 6A, 7A and 8A,

respectively.

PREFERRED EMBODIMENTS OF THE INVENTION As a tire tread element contactsa road surface, it can be shown that the only frequencies generated bythe tread elements are those which are integer multiples of the tirerotation speed. If the tire rotates at revolutions per second, then allof the frequencies in the spectrum will be multiples of 10 cycles persecond. These multiples are called harmonics. Thus, in traditional treaddesigns where equal spacing (no pitching) was used, all of theindividual lugs or pitches contributed to one frequency which producedan exceedingly loud noise. This one frequency has been found to beequivalent to the total number of lugs disposed circumferentially aboutone rib of the tire multiplied by the rotation speed of the tire. Thus,if the tire is composed of 50 lugs equally spaced about the tire, a veryannoying frequency at the 50th harmonic will be heard. At the oppositeend, if it were possible to space the design elements such that eachelement contributed its energy to a different frequency, a quiet,well-tuned tire would result. This ideal noise pattern is termed whitenoise with all harmonic amplitudes at an equal height. Practically, suchan ideal spectrum is unattainable due to other predetermined tread andmold design limitations.

Thus, a compromise must be struck between the whining or whistling soundproduced by an untuned tire and the hishing, background blending soundproduced by the -ideally tuned tire. It has been found that the mostpractical way to generate a tread spacing design has been the trial anderror method such as provided by a computer program adapted for use witha computer terminal connected into a time-sharing computer system. Atread element sequence and pitching ratio may be analyzed according toits corresponding frequency distribution output or spectrum in a matterof minutes. The use of such a computer program significantly speeds uptesting and evaluation of sequences and pitching ratios prescribed bythe present invention. Such a computer program may involve the principalthat one harmonic is examined at a time and each tread element isevaluated for its contribution to that frequency. The program, in turn,may be advantageously based upon the sine and cosine series developed byFourier. It has been found that the use of such a mathematical analysissimulates very closely the actual frequency spectrum as produced by atire on a road surface.

Tread design criteria which will be enumerated hereinafter will beillustrated by considering a tire having only two pitch lengths of thetread design elements. It should be understood that the invention is notintended to be so limited, and in general, applies to tires containing aplurality of pitch lengths. For instance, some tread designs using twobasic pitch lengths may advantageously employ a third, intermediatepitch length to smooth the transition between long strings of short andlong pitches, respectively. This intermediate pitch improves aestheticsand simplifies design of the tread pattern. However, it has been foundquite preferable to employ only two pitches, the advantages includingreduced mold costs, simplicity of design, the ability to use shorterstring lengths than with a greater number of pitches, and to employ agreater number of different string lengths creating greater noisedispersion.

According to the invention, it has been found that there exists acritical relationship between the pitch lengths of the two differentlypitched design elements comprising the tire tread design. Specifically,the pitch ratio of the two design elements must be maintained withinspecified critical ranges. These ranges are defined as the openintervals between successive boundary nodal points given by the relation(n l)/n 1.0, n being an integer selected from 2, 3, 4, 5 or 6. Thus, thepitch ratio between design elements must avoid the ratios /2):l,0,(%):l.0, (%):l.0, (4/5):l.0, and (5/6):l.0. Ranges above (5/6):l.0 areunacceptable because these ratios tend to unduly narrow the bandwidthabout the tread frequency harmonic. This narrow bandwidth of frequenciesabout the tread frequency evidences itself in the form of objectionablenoise. In contrast, the smaller pitch ratios produce broader bandwidthsabout the tread frequency resulting in a desirable modulation of thenoise produced in the vicinity of the tread frequency harmonic.

When the pitch ratio of the design elements is approximately (n-l )/n:l.0, as noted above, there will be a very loud frequency equivalent to:

F=((nl)S+nL)R (1) where,

F frequency in H,

R tire revolutions per second L number of long tread design elements Snumber of short tread design elements It is to be understood thatharmonic frequencies attributable to the undesirable nodal pitch ratiosn l)/n 1.0 are affected solely by the specific pitch ratio and not bysequencing of the pitches or lugs.

While it is necessary only to avoid the nodal points giving a pitchratio of (n l)/n 1.0, it is more preferred to optimize the split innoise energy between any two adjacent nodal frequencies. Thus, themaximum improvement for modulation of frequency peaks attributable tonodal points is attained by utilizing design elements in which the ratioof the shorter tread element to the longer tread element isapproximately (2n 3) /2n l 1.0, n 3, 4, 5 or 6. However, it is quitesuitable to employ a pitch ratio within the range of about onehalf ofthe distance from the preferred ratio of (2n 3 )/2n 1 :l.0, to eachadjacent nodal point, and more preferably, the ratio of shorter pitch tolonger pitch is (2n 3)/2n l 1.0, 20% and most preferably i 5% of thedistance to the next immediate boundary points.

have substantially identical pitch lengths, taking into' considerationmanufacturing tolerances to allow for slight variance in the length ofthe design elements of a particular string. It has been found, accordingto the present invention, that the use of strings of at least 3 and morepreferably of at least 4 consecutive design elements havingsubstantially identical pitch lengths will greatly aid in the modulationof the tread frequency harmonic. The choice of length, as well as thesequential positioning of the strings about the circumference of thetread. can be optimized through testing (such as by utilizing thecomputer program above mentioned) to increase the flattening ormodulation of the tread frequency harmonic. It is preferred that atleast three different string lengths are employed for any given completesequence. Choice of the length of the strings, for instance, will bedictated in part by the pitch ratio. Specifically, higher pitch ratios,e.g. 0.82:1.0, require relatively long strings such as seven to tenconsecutive design elements to effectively modulate the tread frequencyharmonic. In turn, lower pitch ratios such as 06110 demand shorterstring lengths such as four to five consecutive design elements of equallength. The optimum length and sequential positioning of these stringscan be readily determined by those skilled in the art.

In choosing a particular sequence of pitches, it has been found that ingeneral, short strings will reinforce the tread frequency harmonic andlong strings will tend to reinforce the extremes of the tread frequencybandwidth.

In order to better illustrate the invention, reference is made to theaccompanying drawings. In FIGS. 1 2 there is shown a tread portiongenerally designated at 10, which covers a tire casing (not shown)formed in any of a wide variety of forms of construction well known inthe art, such as rubberized fabric or cord plies arranged in a number oflayers. The outer or resilient rubber-like tread portion can be composedof a number of design portions such as indicated within the boundaries12 and 12', the general shape of the design portion repeating itselfcircumferentially about the tire. Each of the design elements or pitchesl2 and 12 as well as the longitudinally running ribs 1'5 and 17 arecomposed of radially outwardly extending lug portions 14, adjacentgrooves 16, sipes 19 and interconnecting fillets 18, the latter providedalong the bottom of a sipe or groove in known manner for the purpose ofreinforcement and to prevent cracking. As shown, each tread designelement may vary in shape or be staggered transversely across the tread,if desired. In the circumferential or longidudinal direction, however,the design elements 12 and 12' have a characteristic pitch length, inthis case, pitch lengths P and P respectively. A portion of the pitchingsequence is shown in each of FIGS. 1 and 2. The pitch length for theseparticular tread designs are measured from the leading edge 20 of thelug portion of a design element to the leading edge 20' of thesucceeding design element.

In FIG. 3, a comparison is made between a 48 pitched tread elementhaving a pitch ratio of the smaller pitch length to the longer pitchlength according to the invention (FIG. 3b, pitch ratio of O.7l4;l.0)and similarly 48 pitched tread elements having adjacent nodal pointsratios (FIG. 3a, pitch ratio of 0.667110; FIG. 3c, pitch ratio of0.75:1.0). 24 pitches are of the shorter length and 24 are of the longerlength. The corresponding predicted frequency spectrums are shownbetween the 100th and 175th harmonics, the area of interest. (Below the100th harmonic, pitch ratio differences are not reflected in thefrequency spectrum in these cases; above the 175th harmonic, cyclingoccurs and the tones are not as audible to the human ear as the lowerharmonics). According to equation 1) above one would predict for FIG. 3aan,

objectionable peak harmonic of (n l) S nL (3 l) 24 3 X 24 48 72 120. ForFIG. 3c one would similarly predict that an objectionable peak harmonicwould occur of the 168th harmonic. These peaks are shown in the figures.They produce loud tones upon rotation of the tire, not only because oftheir high amplitudes, but also because of their relative nakedness,i.e. there do not exist harmonics in the close vicinity of the peakharmonic of sufficiently high amplitude to modulate the tones produced.In comparison, FIG. 3b possesses a modulated spectrum, the peaks at 120and 168 being tolerable because of lower amplitude and the presence ofadjacent harmonics of sufficient amplitude to produce, in effect, adesirable bandwidth of harmonics. In each of FIG. 3a, 3b, and 30identical pitch sequencing was utilized.

FIG. 4 illustrates the effect of too high a pitch ratio in a 48 pitchedtire having 2 pitch lengths of 24 pitches each. The ratio of pitchlengths is 0.84:1.0, above the preferred range according to theinvention. The objectionable feature of the frequency spectrum is thenarrow bandwidth about the tread frequency harmonic (the 48th, equal tothe number of pitches). The tread frequency band is shown as extendingfrom about the 41st harmonic to about the 57th harmonic. In the vicinityof the tread frequency harmonic (or load carrying element harmonic, ingeneral), a narrow bandwidth will produce an objectional tonal noise. Aspreviously mentioned, this bandwidth can be made wider by using apitching sequence containing relatively long strings of pitches. Such asequencing technique was used in FIG. 4 and still the bandwidth, whilemuch improved, could not be widened appreciably more than shown.

FIG. 5 illustrates a typical prior art pitch sequencing scheme for a 50pitched tire. Five different pitch lengths are used and labeled asfollows: 1 0.9; 2 1.0; 3 1.1; 4 1.2; 5 1.3. The sequence is shown inFIG. 5a. Note the short string lengths of one or two consecutive designelements. The frequency spectrum is shown in FIG. 5b; note the strong,deleterious peak at the tread frequency (50th) harmonic.

FIGS. 6 8 illustrate the combined use of a preferred pitch ratio(0.72:1.0) and the effect of various pitch sequences as applied to a 50pitch snow tire. In each of FIGS. 6a, 7a, and 8a, 1 denotes the shorterpitch length and 2 the longer pitch length. In FIG. 6a, two 25 lengthstrings are employed; this produces a wide bandwidth about the treadfrequency harmonic as shown in FIG. 6b, but with relatively highamplitude, non-modulated peaks. In FIGS. and 7b, a refinement isobtained by employing the sequence consisting of a set of alternatingpitches to build up the tread frequency harmonic area, and a set of longstrings (15 in length each) to increase the bandwidth. A furtherrefinement is shown in FIG. 8 in which a mixture of short, intermediateand long strings are employed. A satisfactory degree of modulationresults.

Predicted results using the preferred pitch ratio and sequencingaccording to the invention have been born out using noise analyzers formeasurement of noise produced by a tire rotating upon a driven metalwheel surface. The correlation with the predicted results has been quitegood, despite background noises and low sensitivity of the noiseanalyzing recorder. The predicted results have also been corroborated inactual driving tests. In one such test a Ford Bronco was equipped with aset of traction snow tires having the tire tread sequenced according tothe invention. Another set of snow tires (commercially available) of thesame tread style but having random pitches of three different lengthsand random sequencing (without long strings) was also tested.Qualitatively, the tires made according to the invention were muchquieter overall, and particularly when slowing down and rounding gradualcurves.

While the invention has been explained in particular with reference touse in tire tread design, it generally applies to rotating apparatushaving radially extending (both outward and inward) spaced load bearingelements. An automotive fan would be one example of such an apparatus;the blades of the fan and space between blades would collectively definea design element which would be pitched and sequenced according to theinvention. The invention is also advantageously applied to spacing ofnotches in V-belts. As is well known in the art, V-belts provided withtransversely extending notches along its inner circumference orundercord enables the V-belt to more easily bend about a small diametersheave. As a portion of the belt engages a sheave, the sides of thenotches impact the contiguous driving and driven sheave surfacescreating noise much like a tire tread element striking pavement.Accordingly, the notching is accomplished using the preferred pitchratios and/or sequencing of the present invention, the pitch lengthsbeing measured between successive leading edges of the notches.

The invention is capable of a variety of modifications and variationswhich will be made apparent to those skilled in the art by a reading ofthis specification. All such modifications, variations and otherequivalents are to be included within the scope of the invention asdefined by the claims appended hereto.

What is claimed is:

1. In a tire construction having an outer tread portion divisible into aplurality of discrete design elements extending circumferentially aboutthe tire, not all of said design elements having identical pitchlengths, the improvement comprising:

providing the tire tread with sequenced design elements in which thesequence is characterized by comprising in at least a portion thereof ofa plurality of strings of design elements, each string consisting ofthree or more consecutive design elements of substantially identicalpitch length, the length and sequential positioning of said stringsselected to modulate the tread frequency harmonic produced upon impactof the road by the tire.

2. The construction of claim 1 wherein the design elements have lengthsselected from at least two different predetermined pitch lengths.

3. The construction of claim 1 wherein the longest string contains atleast four consecutive design elements of substantially identicallength, and where the strings are of at least three different lengths.

4. In a rotatable apparatus having generally radially extending, spaced,load carrying elements cooperating with an axis or axes or rotation, theimprovement comprising providing the apparatus with load carryingelements of two discrete pitch lengths, the ratio of the shorter pitchlength to the longer pitch length being (2n3)/(2n-l) 1.0, n 3, 4, 5 or6, plus or minus one-half the distance to an adjacent boundary nodalpoint ratio defined by t/zerelation (n-l)/n 1.0, n being an integerselected from 2, 3, 4, 5 or 6.

5. The apparatus of claim 4 wherein the ratio of shorter pitch to longerpitch is (2n3 )/2nl 1.0, plus or minus of the distance to the nextimmediate boundary nodal point ratio.

6. The apparatus of claim 4 wherein the ratio of shorter pitch to longerpitch is (2n3)/2n-l 1.0, plus 8 or minus 5% of the distance to the nextimmediate boundary nodal point ratio.

7. In a rotatable apparatus having generally radially extending, space,load carrying elements cooperating with an axis or axes of rotation, theimprovement comprising providing the apparatus with load carryingelements of two discrete pitch lengths, the ratio of the shorter pitchlength to the longer pitch length falling within one of the openintervals defined by the boundary nodal point ratios (n-l )/n z 1.0, nbeing an integer selected from 2, 3, 4, 5 or 6, said load carryingelements being sequenced, the sequence characterized by comprising in atleast a portion thereof of a plurality of strings of said load carryingelements, each string consisting of three or more consecutiveload-carrying elements of substantially identical pitch length, thelength and sequential positioning of said strings selected to modulatethe load-carrying element frequency harmonic produced upon rotation ofthe apparatus about its axis of rotation.

8. A tire tread portion comprising:

a plurality of circumferentially extending discrete tread designelements, said elements selected from one of two relative pitch lengths,the ratio of the shorter pitched element to the longer pitched elementbeing (2n3)/2nl 1.0, n 3, 4, 5 or 6, plus or minus one-half the distanceto an adjacent nodal point ratio defined by the relation (nl )ln 1.0, n2, 3, 4, 5 or 6, the design elements of said tread being sequencedcircumferentially about the tire, the sequence characterized bycomprising in at least a portion thereof of a plurality of strings ofdesign elements, each string consisting of three or more consecutivedesign elements of substantially identical pitch lengths, the length andsequential positioning of said strings selected to modulate the treadfrequency harmonic produced upon impact of the road by the tire.

9. The tire tread of claim 8 wherein n 3 to give a pitch ratio of(O.6):l.0.

10. The tire tread of claim 8 wherein n 4 to give a pitch ratio of about(0.714):1.0.

11. The tire tread of claim 8 wherein the ratio of the shorter pitchedelement to the longer pitched element is approximately (2n3 )/2nl 1.0. a

12. In an endless V-belt, the improvement comprisnotching the undercordof said V-belt to produce a series of transverse notches, the distancebetween successive leading edges of the notches defining designelements, said design elements being of two different pitch lengths, theratio of pitch lengths being (2n3)/'2nl 1.0, n 3, 4, 5 or 6, plus orminus one-half the distance to the adjacent boundary nodal point ratiosdefined by the relation (n-l )/n :10, n 2, 3, 4, 5 or 6.

13. The V-belt of claim 12 wherein the notch elements are sequenced thesequence characterized by comprising in at least a portion thereof of aplurality of strings of notch elements, each string consisting of threeor more consecutive notch elements of substantially identical pitchlengths, the length and sequential positioning of said strings selectedto modulate the notch element frequency harmonic produced upon rotationof the V-belt about a driving and a driven sheave.

1. In a tire construction having an outer tread portion divisible into a plurality of discrete design elements extending circumferentially about the tire, not all of said design elements having identical pitch lengths, the improvement comprising: providing the tire tread with sequenced design elements in which the sequence is characterized by comprising in at least a portion thereof of a plurality of strings of design elements, each string consisting of three or more consecutive design elements of substantially identical pitch length, the length and sequential positioning of said strings selected to modulate the tread frequency harmonic produced upon impact of the road by the tire.
 2. The construction of claim 1 wherein the design elements have lengths selected from at least two different predetermined pitch lengths.
 3. The construction of claim 1 wherein the longest string contains at least four consecutive design elements of substantially identical length, and where the strings are of at least three different lengths.
 4. In a rotatable apparatus having generally radially extending, spaced, load carrying elements cooperating with an axis or axes or rotation, the improvement comprising providing the apparatus with load carrying elements of two discrete pitch lengths, the ratio of the shorter pitch length to the longer pitch length being (2n-3)/(2n-1) : 1.0, n 3, 4, 5 or 6, plus or minus one-half the distance to an adjacent boundary nodal point ratio defined by the relation (n-1)/n : 1.0, n being an integer selected from 2, 3, 4, 5 or
 6. 5. The apparatus of claim 4 wherein the ratio of shorter pitch to longer pitch is (2n-3)/2n-1 : 1.0, plus or minus 20% of the distance to the next immediate boundary nodal point ratio.
 6. The apparatus of claim 4 wherein the ratio of shorter pitch to longer pitch is (2n-3)/2n-1 : 1.0, plus or minus 5% of the distance to the next immediate boundary nodal point ratio.
 7. In a rotatable apparatus having generally radially extending, space, load carrying elements cooperating with an axis or axes of rotation, the improvement comprising providing the apparatus with load carrying elements of two discrete pitch lengths, the ratio of the shorter pitch length to the longer pitch length falling within one of the open intervals defined by the boundary nodal point ratios (n-1)/n : 1.0, n being an integer selected from 2, 3, 4, 5 or 6, said load carrying elements being sequenced, the sequence characterized by comprising in at least a portion thereof of a plurality of strings of said load carrying elements, each string consisting of three or more consecutive load-carrying elements of substantially identical pitch length, the length and sequential positioning of said strings selected to modulate the load-carrying element frequency harmonic produced upon rotation of the apparatus about its axis of rotation.
 8. A tire tread portion comprising: a plurality of circumferentially extending discrete tread design elements, said elements selected from one of two relative pitch lengths, the ratio of the shorter pitched element to the longer pitched element being (2n-3)/2n-1 : 1.0, n 3, 4, 5 or 6, plus or minus one-half the distance to an adjacent nodal point ratio defined by the reLation (n-1)/n : 1.0, n 2, 3, 4, 5 or 6, the design elements of said tread being sequenced circumferentially about the tire, the sequence characterized by comprising in at least a portion thereof of a plurality of strings of design elements, each string consisting of three or more consecutive design elements of substantially identical pitch lengths, the length and sequential positioning of said strings selected to modulate the tread frequency harmonic produced upon impact of the road by the tire.
 9. The tire tread of claim 8 wherein n 3 to give a pitch ratio of (0.6):1.0.
 10. The tire tread of claim 8 wherein n 4 to give a pitch ratio of about (0.714):1.0.
 11. The tire tread of claim 8 wherein the ratio of the shorter pitched element to the longer pitched element is approximately (2n-3)/2n-1 : 1.0.
 12. In an endless V-belt, the improvement comprising: notching the undercord of said V-belt to produce a series of transverse notches, the distance between successive leading edges of the notches defining design elements, said design elements being of two different pitch lengths, the ratio of pitch lengths being (2n-3)/2n-1 : 1.0, n 3, 4, 5 or 6, plus or minus one-half the distance to the adjacent boundary nodal point ratios defined by the relation (n-1)/n :1.0, n 2, 3, 4, 5 or
 6. 13. The V-belt of claim 12 wherein the notch elements are sequenced the sequence characterized by comprising in at least a portion thereof of a plurality of strings of notch elements, each string consisting of three or more consecutive notch elements of substantially identical pitch lengths, the length and sequential positioning of said strings selected to modulate the notch element frequency harmonic produced upon rotation of the V-belt about a driving and a driven sheave. 